Random Thoughts on Photography [10] ~ Getting to "linear"

A friend emailed me recently and asked if I knew about linear profiles?

I had to stop a moment and think about it, because I'd not heard it referred to in this way.  

People are working to get to linear curves into certain RentWare.  Remember my comments on "closed systems"?  There are long discussions on the topic of "linearity" in image processing.

If I understand correctly, the re-linearization of RentWare is through the application of a "profile."  The goal being to retain as much highlight tonal separation as possible.  It appears that someone realizes how RentWare strongly raises highlight tones and wants to "re-correct" that.  Raising highlights to make an image look "good" flattens tonal separation.  For example, in landscape photography, think clouds.

Further, if linear profiles are actually camera profiles applied at the initial color management stage, then these must be working to counteract the effects of the software.  Some RentWare uses dcp format files which can have a "curve" built-in.  Perhaps in those cases the camera profile does not specify a "curve."  As you can see, most of this is wild speculation on my part.

In my little Linux/RawTherapee/Gimp world, struggles most often revolve around learning and understanding as there are often fewer and different limits placed on the user.  Generally, I can figure out how things are done in proprietary software and RentWare by studying various on-line guides and such.  So I set out to try and understand this problem of linearity in RentWare.

One of things I learned about processing black and white images in RawTherapee is I get the best results when I don't use any of the automated selections that attempt to make an image look good.  Rather, I take the center of the curve and raise it until the mid-tone and highlight relationships look correct to my way of seeing.  Then I mess around with the "lightness" and "contrast" sliders.

Looking closer I saw that RawTherapee set their starting point at a "linear curve."  This is the default/baseline post-demosaic and post-color-management state.  The man page says...

Linear curve ~ This represents the unaltered (or linear) image, so without any tone curve applied. It disables the curve...

No wonder I didn't understand what the problem was in RentWare and the need for "linear profiles."  I already have and frequently start from a proper linear/flat curve/profile.  As far as I can tell, the problem of linearity doesn't apply to my particular process flow.

Beating a dead horse, RentWare and proprietary software work to give us a good looking image in as few steps as they feel they can get away with.  In so doing they take away a far amount of control early in the pipeline control.  Taken to it's (ill?)logical end, mobile phone image processing takes us even further down the image processing pipeline before it hands control over to us, the user.

One last thought: While I can't really comment on how efficient RentWare re-linearization is, I wonder how much color distortion is being introduced into the process?  If these are dcp format files applied at the color management stage, the RentWare linear profiles probably are just fine.  I couldn't help but ask, that's all.